The present invention is a method for the preparation of allylsilanes. The method comprises contacting magnesium metal with a mixture comprising diethylene glycol dibutyl ether, allyl halide, and a halosilane at a temperature within a range of about 5.degree. C. to 200.degree. C. The method provides a high yield of allylsilane product that is easily recoverable and also provides for high ratios of allylsilane to hexadiene by-product.
The reaction of organic halides with magnesium metal in the presence of solvents such as dialkyl ethers to form reactive complexes typically referred to as Grignard reagents is well known. The production and reactions of Grignard reagents has been the subject of books and numerous review articles. Such reviews are provided, for example, in Coates et al., ORGANOMETALLIC COMPOUNDS, Vol. 1, p. 76-103 (1967), Methuen and Co. LTD, London, U.K.; and in Kirk and Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 10, 721-734 (1966), The Interscience Encyclopedia, Inc., NY, N.Y. The structure of the Grignard reagent has not been determined with certainty. However, it is generally believed that the Grignard reagent exists as a complex in solution and solvent can play a critical role in such complex formation. The unpredictable effect of solvent on the formation and reactivity of Grignard reagents is discussed in the above cited review articles.
The reaction of Grignard reagents with halosilanes is also well known and many such reactions are described in Kharash et al., Grignard Reactions of Nonmetallic Substances, Prentice-Hall, Inc. NY, 1954, P. 1306-1331.
The preparation of 1,5-hexadiene, by a process using an allyl chloride Grignard reagent as an intermediate is known. For example, Turk et al., Organic Synthesis, Vol. 27, 7-8, 1947, teach a process for preparing 1,5 hexadiene by the reaction of allyl chloride in anhydrous ether with magnesium turnings. Turk et al. teach that this reaction results in the formation of a thick slurry which becomes unstirrable. This unstirrable slurry is then treated with a hydrochloric acid solution until the magnesium chloride by-product is in solution and the slurry becomes sufficiently fluid to be stirred.
The process as taught by Turk et al. is not generally acceptable as a commercial process. The formation of the non-stirrable slurry during conduct of the reaction can cause reduced mass transfer and heat transfer and therefore reduced yield of product. Furthermore, the nature of the slurry makes it necessary to treat the slurry in an additional step with a reagent to solubilize the slurry to allow isolation of the product. Typically, a major portion of the product is trapped within the non-stirrable slurry. In addition, the non-flowable nature of the slurry does not allow for the reaction to be run as a continuous process.
Turnbull et al., U.S. Pat. No. 5,358,670, report the formation of alkyl Grignard reagents in diethylene glycol dibutyl ether (DEGDBE). Turnbull et at. reported that Grignard reagents prepared in the presence of DEGDBE have improved yield and stability.
It is an objective of the present invention to provide a method for preparing allylsilanes using a Grignard-type reagent as an intermediate, where the method avoids many of the above discussed problems with Grignard type processes by creating a reaction mixture that is flowable and easily stirred. Thus, mass transfer and heat transfer can be improved in the reaction mixture providing for improved yield of allylsilane. In addition, the method provides for a two-phase system from which the allylsilane can be easily separated. Furthermore the present method provides for an improved ratio of the desired allylsilane to hexadiene by-product, when compared to known Grignard-type processes for preparing organo substituted silanes.